<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        /* 定义id选择器 */
        #blue{
            color: skyblue;
        }
    </style>
</head>
<body>
    <div id="blue">这个div文字是蓝色的</div>
</body>
</html>